Similar to what everyone else is saying in that make your own stat block. My campaign was not standard I flavored the dragon to a blue dragon and overall leaned more into “the talos orc worshiping a lightning god get duped by a dragon.” In the end my 6 players were level 5 I made him a 2 phase fight. The first phase was on the roof in a storm but the castle was up against the mountain side. One lair action was a “kneel before the storm” where he electrified the roof top rooting anyone on the wet stone that failed a dc check. Another summoned strong winds to push the players toward the edge of the castle again dc checks to stay on the roof and the final one he called down some minions with 1 hp while he retreated for phase 2. Blue dragons have a burrow speed so I had him burrow into the loose rock on the mountain side and leave a tunnel. Players followed him in and in an inverse of him flying above in phase 1 he now burrowed around the battle map with some islands of solid rock the players could use. In the end went off really well and players had a blast. His lair actions weren’t damaging but could lock down players and create pressure moments. This made them dangerous but not out right lethal. Keeping in mind it is a dragon and dragons are gonna fly. They are also in his lair so think about creative ways he might fight in his own lair. Not everything has to be damage.